Mufasa: The assembly of the red sequence
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Date
2017Author
Dave, Romeel
Rafieferantso, Mika H.
Thompson, Robert J.
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We examine the growth and evolution of quenched galaxies in the Mufasa cosmo-
logical hydrodynamic simulations that include an evolving halo mass-based quench-
ing prescription, with galaxy colours computed accounting for line-of-sight extinc-
tion to individual star particles. Mufasa reproduces the observed present-day red
sequence quite well, including its slope, amplitude, and scatter. In Mufasa, the red
sequence slope is driven entirely by the steep stellar mass{stellar metallicity relation,
which independently agrees with observations. High-mass star-forming galaxies blend
smoothly onto the red sequence, indicating the lack of a well-de ned green valley at
M & 1010:5M . The most massive galaxies quench the earliest and then grow very
little in mass via dry merging; they attain their high masses at earlier epochs when
cold in
ows more e ectively penetrate hot halos. To higher redshifts, the red sequence
becomes increasingly contaminated with massive dusty star-forming galaxies; UVJ
selection subtly but e ectively separates these populations. We then examine the evo-
lution of the mass functions of central and satellite galaxies split into passive and
star-forming via UVJ. Massive quenched systems show good agreement with obser-
vations out to z 2, despite not including a rapid early quenching mode associated
with mergers. However, low-mass quenched galaxies are far too numerous at z . 1 in
Mufasa, indicating that Mufasa strongly over-quenches satellites. A challenge for
hydrodynamic simulations is to devise a quenching model that produces enough early
massive quenched galaxies and keeps them quenched to z = 0, while not being so
strong as to over-quench satellites; Mufasa only succeeds at the former.